Tahir, Mohammed

Dalarna University, School of Technology and Business Studies, Material Science. (Materialvetenskap, Material Science)

Sjögren, Björn

Swerea MEFOS AB.

2012 (English)Report (Other academic)Alternative title

LOWWEAR varmvalsning WP1 (Swedish)

Abstract [en]

LOWWEAR hot WP 1 consists of three main parts. The first part includes design of in-line wear and temperature profile gauge for strip and plate mills.

The second part is the study of roll wear prediction model for hot strip and plate mills.

The third part includes the evaluation of roll materials (Vancron 40, Sverker 3 (RT60) and Vanadis 23 (ASP23)) with regard to roll wear, surface quality and galling. Roll materials were evaluated experimentally in laboratory and in pilot rolling mill.

The purpose of the first part was to develop a gauge that could be inserted in the mill to measure wear and temperature profiles of both work rolls. This gauge should, be easier and faster to use, than existing gauges and be able to show the shape of the top and bottom roll separately.

The gauge was designed as an adjustable measuring device so that it could measure the work rolls independent of the distance between them, within a range of 50 – 110 mm. The reason for this design feature is that different mills have different possibilities of opening the work rolls and it can also vary from time to time, depending on back-up and work roll diameters at the moment. The goal was set to 45 mm and the initial design had 45 mm but due to different changes in the design it had to be increased to 50 mm. These design changes delayed the making of the gauge and all original design features were not implemented during the project time. This delay was also the reason why this part was stopped by the project committee before it was finished.

The purpose of the second part is to develop a roll wear prediction model to improve the process control systems of rolling mills by developing accurate roll wear prediction models that takes more influential parameters into consideration, among others. This was done on the basis of measured roll-wear. By means of this model roll wear of three roll grades, HSS, HiCr and IC were evaluated.

A modified prediction model was presented where the influence of work roll and strip grades were evaluated. The contribution of roll wear from contact area (work roll /strip) and between work roll and back-up rolls was investigated. Different finishing mill stands with different work roll arrangements,differences of roll wear of the upper and lower rolls, the influence of lubrication with mixed and similar strip grades were also studied. By adjusting the model to different rolling conditions, hot strip mill, plate mills and steckel mills, possibilities of testing the modified prediction model in operation, offline and online, were investigated. Using some industrial adjustments, the modified model was used for research and master thesis projects for industrial applications. This was done for hot strip mills, plate mills and steckel mills.

The third part was a study of roll materials, using four different industrial lubricants, laboratory strip reduction tests and pilot experiments were conducted and analyzed. Currently used roll type ASP23 was used as reference roll in the evaluation. The severe tribological conditions of “strip reduction test” (scratch test) gave some evaluation measures about surface roughness and galling. Scratches due to galling identified easily and the sliding length determined. Vancron 40 shows promising through its “surface coating” which is integrated into the finished tooling material. It also shows high resistance to galling, toward adhesive wear under severe conditions for low and high reductions.

The pilot experiment was conducted in a 4-high rolling mill at Swerea MEFOS. Final thickness, work roll temperature after rolling and surface roughness of the strip and work rolls was measured and evaluated. The tests were conducted with different industrial lubricants. To achieve the proposed final thickness, five passes were rolled with a constant reduction of 25 %. The character of upper and lower work roll during rolling was also examined. Lubrication was applied in controlled form to the upper and lower work rolls and into the roll gap. The pilot experiment confirms that Vancron 40 is a promising material for work rolls, through its good performance in surface roughness and combination of galling resistance and adhesive wear resistance.